A use of mobile communications networks has increased over the last decade. Operators of mobile communication networks have increased a number of base stations in order to meet an increased request for service by users of the mobile communications networks. The base stations typically comprise radio systems for relaying radio signals within a cell of the mobile communications network. It is of interest for the operators of the mobile network to reduce the running costs of the base stations. It is one option to implement the radio system of the base station as an antenna embedded radio system in order to reduce the running costs of the base station. Implementing the radio system of the base station as the antenna embedded radio station reduces a space needed to house the hardware of the base station. Implementing the radio system as an antenna embedded radio system may comprise implementing some of the hardware components of the radio system on a chip. Substantially all hardware components of the radio system may be implemented on the chip, when implementing the radio system as the antenna embedded radio system. The space needed to house the antenna embedded radio system is substantially reduced. Typically an active antenna system, i.e. an antenna array comprising a plurality of antenna elements is not included on the chip. A power consumption during normal operation of the radio system is substantially reduced when implementing the radio system on the chip.
It is of interest to provide a reliable quality of service to an individual user of the mobile network given the increase of the number of users of the mobile network. Furthermore the number of users of the mobile network within the cell of the mobile network has increased concomitant to the increase of the number of users of the mobile network.
A radio signal relayed by the radio system located at the base station maybe repeatedly scattered before reaching the user. In other words there are several paths along which the radio signals may travel when reaching the user. Constructive and destructive interferences may occur in situations wherein the radio signals may reach the user along a plurality of paths. Whereas the constructive interference may be of advantage and help improving the quality of service provided to the individual user, the destructive interference will undoubtedly deteriorate the quality of service provided to the individual user.
Several techniques have been suggested in order to deal with the increased number of the users within the mobile network and hence within the cell of the mobile network. Time division multiplexing architectures (TDMA) were suggested as well as frequency multiplexing strategies. Unfortunately both multiplexing techniques are not adapted to compensate the effect of the destructive interferences users experience within the cell of the mobile network. In other words the plurality of paths along which the radio signals travel to reach the user is not eliminated by using the multiplexing schemes.
Typically, the radio station relays the radio signals to a plurality of users within the cell of the mobile network. The individual user will experience the radio signals relayed to other users within the cell as a background noise to the radio signal that is dedicated to the individual user.
A direct line of sight between the radio system and the user with no destructive interference is an ideal condition to provide the best possible quality of service to the individual user.
A scheme of opportunistic beam forming is known in the art. Opportunistic beam forming requires all handsets (of the users) to report a quality of service to the radio system located at the base station. Therefore contemporary protocols of mobile communication such as UMTS (short for Universal Mobile Telecommunications System or HSDPA (short for High Speed Downlink Package Access) allow for a pilot data package to be transmitted to all the users. In response the handsets will measure a signal to interference and noise ratio (SINR) for the pilot data packet and return the SINR value back to the radio system. The radio system will then relay the radio signal intended for the user with the optimal SINR conditions. It may appear unfair to select the individual user being served by the radio system as the user with the optimal SINR value. The optimal SINR of the individual user corresponds to a direct line of sight between the individual user and the radio system. With a plurality of users present within the cell of the mobile network and the users being mobile within the cell, the concept of opportunistic beam forming theoretically reaches the limit of a data throughput defined by a direct line of sight to each one of the individual users.
The opportunistic beam forming requires a sufficiently large number of users in order to be fair. Furthermore fluctuations of the SINR help the opportunistic beam forming to be fair and to reach the limit of the data throughput defined by the direct line of sight to each one of the individual users. With the opportunistic beam forming the radio system just addresses the user that currently has the optimal SINR, hence the name opportunistic beam forming For a detailed introduction to opportunistic beam forming see “Opportunistic Beamforming Using Dumb Antennas” by P. Viswanath, D. Tse, R. Laroia in IEEE Transactions on information Theory, vol. 48, No. 6, June 2002.
The advent of high speed data services in mobile networks creates new challenges for the system operators. It is now necessary for the radio system to provide the radio signals according to very different transfer protocols depending on whether the radio signals comprise voice communication or high speed data communications.
Opportunistic beam forming as in the prior art requires substantial changes to the hardware of the radio system in order to reduce an effect of destructive interferences within the cell of the mobile network.